Chapter 11 of 22 · 3925 words · ~20 min read

Part 11

This cautious policy, rather than the bold and liberal course which the maritime genius of the country demands, condemned us for long years to inaction, until, at length, the absolute necessity for the renewal of a portion of our naval force produced the "Minnesota" class of frigates. Although they developed little that was absolutely new, they are very far from being imitations; but in model, capacity, equipment, and above all in their armament, they have challenged admiration throughout the world, and called from a distinguished British admiral in command the significant declaration, that, until he had seen them, he had never realized his ideal of a perfect man-of-war.

A leading idea in the conception of these ships was to reduce the number of gun-decks from two and three to a single deck, and, consequently, the space in which shells could be lodged. This is a consideration which must, it is believed, sooner or later govern in naval construction; although France and England, long accustomed to measure the power of ships by the number of gun-decks, may be more slow in following our lead in this respect than in imitating the increased calibre of our ordnance.

The new classes of steamers preparing for sea, of which the Hartford and Iroquois are types, promise to be most efficient ships, and to reflect much credit upon our naval authorities for their bold, yet judicious departure from traditions which had long hampered the administration of this important branch of the public service. Although the reflection is seldom made, it is nevertheless true, that much of the reputation enjoyed and of the influence exercised by the United States is due to the efficiency of her navy; and if these are to remain undiminished, then it is of the utmost consequence that the national ships should always represent the highest advancement of nautico-military science.

[Footnote 1: A series of experiments with the screw were made on board the Dwarf in 1845, and on board the Minx in 1847 and 1848, but the results did not materially differ from those previously obtained. In the Rattler, Dwarf, and Minx twenty-nine different propellers were tried.]

The efficiency of the screw having been demonstrated, it was seen that the next requirement for a war-steamer was to place her machinery below the waterline; and hence arose a demand for an entirely new description of engines, which it was clear would make a great change in all the labors of the engineer and machinist. Such change it was evident would greatly enhance the risk of failure, and therefore it was determined by the Admiralty to insure success in this very difficult task by enlisting all the best talent of the country. Accordingly, for the twenty-three ships an equal number of screw engines were ordered; and as with the constructors, so with the engineers, each was required to comply with certain conditions, yet each was permitted to put forth his own individuality, and each has illustrated his views of what was required by a distinct plan of engine.

The wise and liberal action of the British Admiralty, which faltered at no expense, and made trial of every improvement in machinery that gave assurance of good performance and promised in any way to increase the efficiency of the fleet, produced no less than fourteen distinct varieties of the screw engine. Among them all, Penn's horizontal trunk-engine appears to be the favorite, and had performed so well in the Encounter of fourteen guns, the Arrogant of forty-six, the Impérieuse of fifty, and the Agamemnon of ninety, that two years ago it had been placed, in about equal proportions of two hundred, four hundred, six hundred, and eight hundred horse-power, on board of forty ships and many smaller vessels of the British navy; it had fulfilled all the promises made for it, without in any instance requiring repairs. These engines comply with all the conditions reasonably demanded in the machinery of a man-of-war; they lie very low, and the fewness and accessibility of their parts leave scarcely anything to be desired;--a lighter, more compact, or more simple combination has yet to be conceived.[1]

In all the ships above referred to the connection of the engines is direct, and many of them are driven at rates varying from fifty to seventy-five revolutions. This point is dwelt upon because it is observed that many engineers find difficulty in freeing themselves from early impressions made by long-stroke engines, express apprehensions at fifty and sixty revolutions, and stand ready to obviate the difficulty by gearing,--which it is hoped may not henceforth be adopted in our national ships. Geared engines are much heavier than those of direct connection, and occupy more space,--a great consideration in ships where room for fuel is in such demand, besides making it more difficult to place them below the waterline,--a consideration which in men-of-war should be regarded of paramount importance, as the engines of a war-steamer should be as secure from shot as her magazine. Experience has shown that the apprehensions entertained from the quick stroke of direct engines were without foundation; and that, in auxiliary ships, with a properly modelled propeller, there will be no necessity for a very high speed of piston.

The form of engine generally adopted with great success in the later screw-ships.

[Footnote 1: "Its large amount of friction" is an objection often speciously urged against the trunk-engine, although the friction diagram shows it to be actually less in this than in most other engines.] of the United States navy is the "horizontal direct action," with the connecting-rod returning from a cross-head towards the cylinder; these engines make from sixty to eighty revolutions per minute. The steam-valve is a packed slide with but little lap, and the expansion-valve is an adjustable slide working on the back of the steam-valve. The boilers are of the vertical water-tube type, with the tubes above the furnaces, and are supplied with fresh water by tubular surface-condensers, which, together with the air-pumps, are placed opposite the cylinders.

While the vessels ordered by the Admiralty were on the stocks, it was suggested by Mr. Lloyd that the model of their after-bodies was not that most favorable to speed,--that they were too "full," and that a "finer run" would be preferable. To settle this question, the Dwarf, a vessel of fine run, was taken into dock, and her after-body filled out by three separate layers of planking, so as to give it the form and proportions of the vessels then building. These layers of planking could be removed in succession, and the effects of a fuller or finer run upon the speed of the vessel easily ascertained. A trial was then made, and the result proved the correctness of Mr. Lloyd's opinion; the removal of the different layers of planking increasing the speed from 3.75 to 5.75, to 9, and finally to 11 knots. A trial between the Rifleman and the Sharpshooter, vessels of four hundred and eighty tons and two hundred horse-power, and the Minx and Teaser, of three hundred tons and one hundred horse-power, gave similar results,--the speed in each trial being twenty-four per cent. in favor of the finer run.

Although great efficiency and economy had now been attained, there was still an important defect to be remedied, namely, the impediment to speed and to evolution under sail presented by the dragging propeller; which was accomplished by the invention of the "trunk" or "well," into which the propeller can be raised at pleasure; and there is no longer anything to prevent the construction of a screw-frigate which shall be fit to accompany, under canvas only, a fleet of fast sailers, with the assurance that she may arrive at the point of destination in company with her consorts, having in reserve all her steam-power.

The mechanism by which the emersion of the screw is effected is as follows:--There are two stern-posts; between these, and connecting them with each other and with the keel, is a massive metallic frame, in which rests another frame, or _châssis_, in which the screw is suspended; near the water-line, the deck and wales are extended to the after stern-post, and through an opening or trunk in this overhanging stern the frame suspending the screw is raised by worms, working in a rack secured to the frame, and operated from the deck, as shown in the accompanying drawing,--or by a tackle, as is now most common. In the British ship Agamemnon, of ninety guns, the propeller is raised by a hydrostatic pump,--a neat arrangement, but liable to get out of order. When it is desirable to raise the propeller, the blades are first placed in a vertical position, and the operation of lifting is performed in a few minutes.

The relative advantages of the propeller fitted to lift, and that which is permanently fixed, have long been the subject of much discussion.

For merchant steamers, having an established route to perform, on which the aid of steam is in constant demand, it is generally conceded that the position of the screw should be permanent. The construction of the ship is then less costly, while greater strength is preserved; and as these vessels are out of port but for short intervals, should repairs be needed, they have access to the docks. But for men-of-war the case is widely different. Having frequently to keep the sea for long periods, much under canvas, and often far distant from a dock-yard, they should be provided with the means of lifting the screw to repair or to clear it, or to be relieved from the impediment it offers to sailing and to evolution, and also from the injurious "shake" occasioned by a dragging propeller.

[Illustration: MODE OF LIFTING SCREW.]

On the other hand, the construction of a trunk or well impairs the solidity of the stern, renders it much more vulnerable, and weakens its defences, while it opposes to speed the very considerable resistance of the after stern-post.[*] Nevertheless, no modern ship of the British navy is without the means of raising her propeller, and the best opinion of commanders and engineers of that service, of longest experience in screw-ships, goes to establish the conviction, that, for men-of-war, the advantages of being able to lift the propeller far more than outweigh the objections urged against lifting. In this connection we mention the fact, that all screw-ships "by the wind" have a strong tendency to gripe. Would not this be obviated by having a gate or slide to fill out the dead-wood when the screw is lifted?

[Footnote *: Might not a metallic stern-post, combining strength, lightness, and little resistance, be introduced?]

The best illustration of the effects of a dragging propeller was afforded on the departure of a Russian squadron from Cronstadt, bound to the Amoor, in 1857-'58, consisting of three sloops of war bark-rigged, and three three-masted schooners, under the flag of Commodore Kouznetsoff. The vessels of each class were built from the same moulds, and at the time of the experiment were of the same draft and displacement. On clearing the land, signal was made to lift screws and make sail. Soon after, all the squadron reported the execution of the order, except the Voyerada sloop, which had the misfortune to break a key in the couplings, and therefore could not lift her screw. Every effort was tried to get out the key, and meanwhile a very instructive example was presented to the squadron of the effect of a dragging propeller on the speed of the vessel. The circumstances were as follows:--The wind, a gentle breeze, right aft; the Voyerada carrying all sail but the main course; the other two sloops holding way with her with their topsails on the cap, and the schooners with their peaks dropped. Under these conditions, the Voyerada, having her screw-blades fixed horizontally, could scarcely keep her position, running two and a half and three knots. The Voyerada next succeeded in getting her screw vertical, when, without any change in the wind, the speed increased to four and a half knots. The other sloops then mastheaded their topsails, and the schooners peaked their gaffs. At length the Voyerada succeeded in lifting her screw, when immediately all the sloops under the same canvas continued their course, making six to six and a half knots. A better example of the obstruction offered by a dragging propeller could not have been afforded.[1]

The "shake," to which reference has been made, is the tremulous or vibratory motion communicated to the after-body of the ship, and

## particularly to the stern, by the revolution of the propeller, often

opening the seams, and in old ships sometimes starting the butts and causing dangerous leaks. This movement arises from two causes,--one inherent in the screw, the other due to its position in the deadwood. The first cause is the difference in the propelling efficiency of the upper and lower blades when in any other position than horizontal. The centre of pressure of the lower blade, being at a greater depth below the surface than the centre of pressure of the upper blade, acts upon a medium of greater resistance to displacement, and the differential of the pressures of the two blades produces inevitably a vibratory motion in the stern of the vessel. This effect is greatly increased when the clearance given to the screw in the dead-wood is too small; for the reduction of the hydrostatic pressure at the stern-post, and the increase of it at the rudder-post, on each passage of the blades, must be followed by concussion. Therefore, if the "well," or distance between the posts, be made sufficiently long in proportion to the screw, the "shake" due to the latter cause can be almost entirely obviated.

In 1851, the British Admiralty selected three auxiliary screw-ships, of different classes and qualities, for an experimental cruise, namely:--

[Footnote 1: _Russian Nautical Magazine_, No. XLI., December, 1857.]

They were ordered to pass round the Azores, each ship holding her course, and using sail or steam, or both, as was deemed most advantageous. An officer was sent on board each ship to keep a record of her performance, and to note the time when and the position where, the coal being entirely consumed, the contest ended. In this trial, the Arrogant was found superior to the Dauntless, and both of them far excelled the Encounter; indeed, no very different result was expected, the object of the trial being to ascertain their relative as well as positive value. These ships afterwards formed a part of the experimental squadron stationed at Lisbon in the same year, which was composed of the finest ships in the British navy.

It was believed by many officers, that a fast-sailing frigate, in a reefed-topsail breeze, would be able to get away from any screw-ship; but in a trial that took place between the Arethusa and the Encounter, and the Phaëton and Arrogant, under circumstances the most favorable to the sail-ships, it was found that the screw-ships, using both steam and sail, had decidedly the superiority,--and that in fresh gales, with one, two, or three reefs in the topsails, either "by the wind," or "going free," the Phaëton and the Arethusa, the fastest sail-frigates in the navy, were always beaten by the Arrogant. This result operated powerfully in removing the repugnance to steam existing among all classes of seamen; and the vast superiority of well-organized screw-ships for the purposes of war is now so apparent, as to render them the most important and indispensable part of every navy.

While the English were engaged in the trials here related, their rivals on the opposite coast were not indifferent spectators. The French were nearly as soon in the field of modern screw experiment as their neighbors; and did the limits of this paper permit, it would be instructive, as well as interesting, to trace the ingenious and persevering steps by which they also approached the solution of that difficult problem, the construction of a screw-man-of-war.

The first result of their efforts, La Pomone, screw-frigate, was shown to the world in 1844, and after careful inspection, (in 1853,) it is affirmed, such was the perfection of her general organization, that she has hardly been excelled by any of her younger sisters.

The most complete course of experiments ever made, perhaps, with the new motor, was that carried out by MM. Bourgois and Moll, of the French navy, in 1847 and '48, which they verified by a second series in 1849. These experiments were instituted to ascertain the relative efficiency of all varieties of the screw-propeller, upon vessels of different models and dimensions, and under all the varying conditions of wind and sea, in order to determine the propeller best adapted to each particular description of ship.[*]

Necessarily brief as is the notice of Gallic ingenuity and skill, the acknowledgment must be made, that, for the invention of the trunk or well, with its attendant advantages, navigation is indebted to Commander Labrousse, of the French navy; and for a novel arrangement of the screw- propeller, which has not attracted all the notice it deserves, obligations are due to M. Allix, a distinguished engineer of that service; and the propeller more recently introduced by M. Mangin, of the same corps, if it performs all that is claimed for it, namely, that it does away with the "shake," will be of great value.

[Footnote *: For a most interesting and instructive memoir upon these experiments, the reader is referred to that admirable work, by Captain E. Paris, of the French navy, _L'Hélice Propulsive_.]

In concluding this recognition of the contributions by France to screw-propulsion, it is desired to submit a few general observations on the French navy; for, although upon every sea the tri-color waves over ships proudly comparing with those under any other flag, it is nevertheless too commonly believed that the docks of France are crowded and her navy-list swollen with hulks which are but the mouldering mementos of the vast armaments hastily created during the Consulate and the Empire; an illusion most hazardous to our interests abroad and our security at home.

At the period of _the coup d'état_ of 1851, a Committee of Inquiry, composed of the most experienced and intelligent officers and distinguished legislators, had visited all departments of the navy, and made the most careful investigations into every branch of the service. Upon the evidence thus obtained, a report was submitted, providing for the improvement of the condition of the officers and seamen, and the increase, renewal, and remodelling of the _matériel_,--in fine, for the correction of every abuse, the remedy of every evil, and the development of all good existing in the navy. This report, stamped on every page with patriotism and intelligence, commanded, even in the midst of revolution, the support of all parties, the adhesion of every faction; and has since, through all changes in the Ministry of the Marine, formed the basis of the action of that department.

Under these auspices, France has in the last seven years organized the means of promptly putting to sea a numerous fleet, composed of the most modern and most powerful steamers, manned by efficient crews, commanded by skilful officers; and now worthily maintains a position as a naval power second only to that of Great Britain. At this moment, whilst the British fleet includes but thirty-six screw line-of-battle ships, mounting 3,400 guns, and propelled by 19,759 horse-power, that of France may boast of forty such ships, mounting 3,700 guns, propelled by 27,500 horse-power; and while England has but thirty-eight screw-frigates, France has forty-two.

In thus briefly summing up the forces of our ocean rivals, we cannot avoid making some reflections suggested by the unpreparedness of this country to meet any sudden burst of hostility. This not only involves the risk of national humiliation, but paralyzes our diplomacy; since it deprives us of that influence among the nations, which otherwise--from the breadth of our territory, the value of our products, the activity of our industry, the importance of our commerce, and the extent of our maritime resources--we of right should hold.

No country is more interested than the United States in the maintenance of peace; yet, even on the principle of economy, we may argue in favor of a degree of preparation for war; for that calamity may best be averted by taking from foreign powers the temptation to interfere with us: all history showing that the justice and friendship of military states are but slender guaranties for the peace of a nation unprepared for attack.

It is vain to talk of husbanding financial resources for war, without other preparation. When once embarked in hostilities, and in a position to maintain our ground, large finances, judiciously used, will ultimately command success; but no accumulation of funds can provide a timely remedy for that weakness which cannot resist the first blow.

The national safety should no longer be left to chance, but be established on a basis of certainty. A navy cannot be manufactured nor a fortress built to meet an emergency, but should be kept ready-made.

In considering the auxiliary screw-frigate under the views already offered, and in determining the canvas with which she should be supplied, it will be well to refer, as the best guide, to the fastest sail-ships,--the class which presents the greatest similarity in form to that demanded in screw-ships. In these ships the great length of deck offers every facility for the most advantageous spread of canvas; consequently the centre of effort may he kept low, and the requisite power and stability combined.

Intimately connected with her sailing-power is another branch of the equipment of a screw-ship, which requires the most earnest, patient, and intelligent consideration. Prepared to endure all the wear and tear of a sail-ship, she should at the same time be ready for transmutation into a steam-ship; namely, when, for any urgent service, her best powers of steaming are required, she should be able to divest herself speedily of yards and top-masts, and, the special service completed, resume all her perfection as a sail-ship.

It would be out of place here to enter into details of equipment. In naval affairs nothing is improvised, and a satisfactory conclusion upon these points can be arrived at only through long experiment, and perhaps frequent disappointment. Yet it is not doubted that the same ship may exhibit a handy and efficient rig, develop a high velocity canvas, and, without great power, a sufficient speed under steam.

In our navy, away from our own coast, sail must of necessity be the rule, and steam the reserve or special power; and without abandonment of our anti-colonial policy--with the depots of our rivals upon every sea, yet not a ton of coal upon which we can rely--we should not dare to send abroad a single ship which, whenever she gets up her anchor, must needs also get up her steam.